Since hydrogen sulfide has long been known to be a very toxic and malodorous gas, considerable efforts have been expended to develop methods for its removal from gas streams. Various common sources of hydrogen sulfide, such as sewage gases and the effluents from kraft pulp mills, also contain other odorous components, for which activated carbon is an effective purification medium. However, the breakthrough capacity of activated carbon for hydrogen sulfide is relatively low compared with its breakthrough capacity for most organic vapors, and for this reason the carbon is generally treated in some way to enhance its breakthrough capacity for hydrogen sulfide. One of the treatments involves the impregnation of the activated carbon with sodium hydroxide (caustic soda), as described in U.S. Pat. No. 4,072,479, or with potassium hydroxide (caustic potash).
Another method involves the addition of ammonia to the air stream containing the hydrogen sulfide prior to its passage through the unimpregnated activated carbon, as described in U.S. Pat. No. 4,615,714.
Although caustic impregnations bring about a significant increase in the breakthrough capacity of the carbon for hydrogen sulfide, any additional such capacity would be very desirable.